(1) Field of the Invention
The present invention relates to a catalyst for polymerizing .alpha.-olefins with which poly-.alpha.-olefins having a high degree of stereoregularity are produced with the aid of the catalyst comprising a titanium component of the so-called carrier type and an organic aluminum compound.
(2) Description of the Prior Art
Recently, a method for improving the activity of a Ziegler-Natta catalyst by supporting its titanium component on a carrier has been developed. One example of the prior art concerned therewith is proposed in Japanese Laid-Open Patent Publication No. 9342/72 which discloses a method for improving the stereoregularity of the resulting polymer by adding an electron donative compound as the third component to a combination of a carrier type titanium component (composed of a titanium compound supported on a magnesium halide) and an organic aluminum compound.
However, if propylene is polymerized in the presence of such a conventional two-component catalyst comprising a carrier type titanium component and an organic aluminum compound, the crystallinity of the resulting polymer is extremely low despite the high polymerization activity of the catalyst. Although the crystallinity of the resulting polymer is improved by adding an electron donative compound to the catalyst, the polymerization activity of the catalyst is remarkably lowered. Moreover, the effect of improving the crystallinity of the resulting polymer is not satisfactory because it is difficult to produce crystalline polypropylene which is equal in quality to that obtained with the aid of a catalyst (for example, a titanium trichloridediethylaluminum monochloride catalyst) in current use for industrial purposes.
In the process disclosed in Japanese Laid-Open Patent Publication No. 126590/75, there is proposed a catalyst composed of a composition obtained by reacting a co-comminuted mixture of a magnesium halide and an organic acid ester with titanium tetrachloride; an organic aluminum compound; and an organic acid ester. However, this catalyst is unsatisfactory from the viewpoints of both its polymerization activity and the crystallinity of the resulting polymer.